1. Field of the Invention
This invention is directed to phase detector systems, in general, and to circuits for automatically nulling the offset error signal frequently found therein, in particular.
2. Prior Art
There are many types of circuits wherein a particular phase or frequency signal is necessary and/or desirable. In order to lock on to this signal, it is frequently found advantageous to use a phase-locked-loop. However, in the past the phase-locked-loop circuits have included various components, for example, operational amplifiers, which produce error signals as a result of offset voltages at the input terminals thereof.
Various approaches and techniques have been utilized in an attempt to avoid or null the offset or error signal. However, these techniques have usually been quite cumbersome and provided as many problems as they have provided solutions. Typically, the initial adjustment to compensate for the error signals is impermanent at best and varies with time, temperature, aging and the like. Consequently, a new technique for avoiding the offset error signal is highly desirable.